1. Field of the Invention
The present invention relates to an apparatus and method for heating a substrate, and a coating and developing system employing the heating apparatus.
2. Description of the Related Art
A known coating and developing system coats a substrate (e.g., a semiconductor wafer, or a glass substrate for a liquid crystal display) with a resist solution and develops an exposed resist, in order to form a resist pattern on the substrate. Such a coating and developing system employs a heating apparatus that is generally called “baking apparatus”. The baking apparatus heats a wafer coated with a resist solution to vaporize a solvent contained in a resist solution to dry the resist solution.
FIG. 18 shows the structure of a heating apparatus in one example. Reference numeral 10 denotes a casing, and reference numeral 10a denotes a wafer delivery port. Reference numeral 11 denotes a base, and reference numeral 12 denotes a cooling plate for cooling a wafer adapted to move toward a hot plate 12a. Drive mechanisms 13 and 14 are arranged in a space below the base 11 to vertically move pins 13a and 14a, respectively. The vertical movement of the pins 13a by the drive mechanism 13 allows a wafer to be transferred between the cooling plate 12 and a not shown wafer conveyer that enters the casing 10 through the wafer delivery port 10a. The vertical movement of the pins 14a by the drive mechanism 14 allows a wafer to be transferred between the cooling plate 12 and the hot plate 12a. The drive mechanism 14 is arranged outside an area right below the hot plate 12a in order to avoid deterioration of the drive mechanism due to thermal radiation emitted from the hot plate 12a. JP1-242124A discloses such an arrangement of the drive mechanism, for example. In FIG. 18, reference numeral 15 denotes a top plate, which moves vertically by a drive mechanism 15a and functions as a cap or a cover. Reference numeral 16 denotes an area in which electric components for operating the drive mechanism 15a are installed.
When a wafer W is placed on the hot plate 12a, the top plate 15, which serves as a flow guide and is arranged above the base 11, descends to contact closely to the peripheral portion of the base via an O-ring 15b to define a sealed space around the wafer W. Thereafter, a gas supply unit 17a supplies a gas into the sealed space through a circumferentially-arrayed, gas supply ports 17, while a suctioning unit 18a evacuates the sealed space through a suctioning port 18 arranged at the central portion of the top plate 15. Thereby, the wafer is heated while the gas flows from the peripheral portion towards the central portion of the wafer W.
The aim of defining the sealed space around the wafer W is to keep the lower surface of the top plate 15 at a certain high temperature. If the temperature of the lower surface of the top plate 15 is lowered, the main flow of the gas is disturbed by local updraft and/or downdraft generated due to temperature difference between the hot plate 12a (or wafer W) and the top plate 15, resulting in deterioration of in-plane temperature uniformity of the wafer W. If such a disturbed flow occurs, sublimed resist components are likely to be adhered to the top plate 15, and thereafter possibly fall onto the wafer W to contaminate the same.
The heating apparatus of FIG. 19 with the movable top plate 15 must be provided with a driving mechanism for the top plate 15, and thus is large-sized and has a complicated structure. Moreover, if sublimed components are adhered to the top plate 15, the sublimed components may possibly fall onto the wafer due to the vibrations generated by the vertical movement of the top plate 15, resulting in contamination of the wafer W.
In order to achieve in-plane uniformity of a heat treatment without using a vertically-movable top plate, a possible solution is the provision of a heater in the top plate for heating the lower surface thereof.
In some cases, such a heating apparatus heats wafers of different process lots at different temperature. For example, the process temperature of wafers of a first lot is 150° C., and the process temperature of wafers of a second lot is 130° C. In this case, the top plate must be cooled after the completion of the process of first-lot wafers, in order to prevent the second-lot wafers from being heated at an excessive high temperature. However, the top plate provided with a heater has a high heat capacity, and thus a considerable long time is required to cool the top plate, resulting in a reduced throughput of the heating apparatus.
JP8-45817A discloses a baking apparatus for baking a substrate coated with a chemical amplification resist after exposure. When the substrate is baked in the baking chamber, the chamber is filled with an inert gas. The baking chamber is defined by heat-insulating walls each having a vacuum insulating layer, which stabilizes the temperature in the baking chamber to achieve a desired diffusing condition of an acid component produced in the resist by baking the resist. The apparatus of JP8-45817A differs from the apparatus of FIG. 19 in that the former does not employ a gas flow to promote the baking treatment of the resist. JP8-45817 does not provide any solution to the foregoing problems associated with the apparatus of FIG. 19.